Costs of immune defense: an enigma wrapped in an environmental cloak?

Costs of immune defense: an enigma wrapped in an environmental cloak?

Host defense against parasites and pathogens has been recognized as a costly life-history trait that can generate trade-offs with other fitness components. However, universality of immunological costs and associated trade-offs remains questionable in animal–parasite systems. This discrepancy could be a result of environmental effects, which have the potential to modulate the detection of trade-offs associated with immune function. Here, attention is drawn to the role that environmental factors can play in the manifestation and detection of costs associated with immune function and resistance. Moreover, we stress the importance of considering multiple external factors, host ontogeny and estimates of immunological function in studies investigating immune-related costs in animals.